Acre
An acre is a customary unit of area equal to exactly 4,046.8564224 square metres. Its size is independent of its shape.
Square metre: The SI unit of area, equal to the area of a square one metre on each side. The acre’s exact definition is stated as a number of square metres.
Anglo-Saxon units of measurement: Units of length, area, and capacity used in England before the Norman Conquest. The acre developed from earlier English land measures.
Land surveying: The measurement and mapping of land boundaries, elevations, and features. Surveyors calculate parcel areas in acres where customary units are standard.
Hectare: A metric unit of area equal to 10,000 square metres. The hectare is the common metric alternative to the acre.
Square mile: A unit of area equal to the area of a square one mile on each side. A square mile contains 640 acres, placing the acre within a larger land measure.
Furlong: A traditional unit of length equal to 660 feet or one-eighth of a mile. The traditional acre was conceived as a strip one furlong long.
Cadastral map: A map showing land parcels, boundaries, and ownership information. Cadastral records often report parcel areas in acres.
Are (unit): A metric unit of area equal to 100 square metres. The are is a smaller metric land-area unit with a decimal relation to the hectare.
Square foot: A unit of area equal to the area of a square one foot on each side. One acre equals 43,560 square feet, connecting the unit to smaller customary measures.
Chain (unit): A surveying unit of length equal to 66 feet. A square chain contains one-tenth of an acre, linking the unit to later surveying practice.